Add interpreter for AllGatherOp

[ghpvnist]

We have the following constraints in the spec:

(I1) `operand`: tensor or per-tensor quantized tensor.
(I2) `all_gather_dim`: constant of type `si64`.
(I3) `replica_groups`: 2-dimensional tensor constant of type `si64`.
(I4) `channel_id`: constant of type `si64`.
(I5) `use_global_device_ids`: constant of type `i1`.
(C1) `0 <= all_gather_dim < rank(operand)`.
(C2) `is_unique(replica_groups)`.
(C3) `size(replica_groups)` is defined as:
* `num_replicas` if `cross_replica` is used.
* `num_replicas` if `cross_replica_and_partition` is used.
* `num_processes` if `flattened_ids` is used.
(C4) `0 <= replica_groups < size(replica_groups)`.
(C5) If `use_global_device_ids = true`, then `channel_id > 0`.
(C6) `type(result) = type(operand)` except:
* `dim(result, all_gather_dim) =
  dim(operand, all_gather_dim) * dim(process_groups, 1)`.

These constraints will be comprehensively covered by the following tests:

I1: a) `operand` is not a tensor. (Covered by ODS).
I2: a) `all_gather_dim` is not a constant of type `si64`. (Covered by ODS).
I3: a) `replica_groups` is not a 2-dimensional tensor constant.
I3: b) `element_type(replica_groups) != si64`. (Covered by ODS).
I4: a) `channel_id` is not a constant of type `si64`. (Covered by ODS).
I5: a) `use_global_device_ids` is not a constant of type `i1`. (Covered by ODS).
C1: a) `all_gather_dim < 0`.
C1: b) `all_gather_dim >= rank(operand)`.
C2: a) `is_unique(replica_groups) = false`.
C3: a) `size(replica_groups)` is defined as:
* `num_replicas` if `cross_replica` is used.
* `num_replicas` if `cross_replica_and_partition` is used.
* `num_processes` if `flattened_ids` is used. 
C4: a) `replica_groups < 0`.
C4: b) `replica_groups >= size(replica_groups)`.
C5: a) `use_global_device_ids = true` and `channel_id <= 0`.
C6: a) `type(result) != type(operand)` except:
* `dim(result, all_gather_dim) =
  dim(operand, all_gather_dim) * dim(process_groups, 1)`.

If we drop the "Covered by ODS" pieces, this will leave us with the following test cases:

I3: a) `replica_groups` is not a 2-dimensional tensor constant.
C1: a) `all_gather_dim < 0`.
C1: b) `all_gather_dim >= rank(operand)`.
C2: a) `is_unique(replica_groups) = false`.
C3: a) `size(replica_groups)` is defined as:
* `num_replicas` if `cross_replica` is used.
* `num_replicas` if `cross_replica_and_partition` is used.
* `num_processes` if `flattened_ids` is used. 
C4: a) `replica_groups < 0`.
C4: b) `replica_groups >= size(replica_groups)`.
C5: a) `use_global_device_ids = true` and `channel_id <= 0`.
C6: a) `type(result) != type(operand)` except:
* `dim(result, all_gather_dim) =
  dim(operand, all_gather_dim) * dim(process_groups, 1)`.

Notes:

• C3a verification is infeasible since num_replicas and num_partitions are not known statically.
• C4b verification is infeasible since size(replica_groups) is not known statically.

closes #1118